A flywheel is mounted on the crankshaft of an engine in order to absorb vibrations caused by combustion fluctuations in the engine. A clutch device is provided on the transmission side in the axial direction of the flywheel. The clutch device includes a clutch disk assembly coupled to the input shaft of the transmission, and a clutch cover assembly that biases a friction coupling component of the clutch disk assembly to the flywheel. The clutch disk assembly has a damper mechanism to absorb and damp any torsional vibration. The damper mechanism has a coil spring or other such elastic member disposed so as to be compressed in the rotation direction.
Another known structure is one in which a damper mechanism is provided between the crankshaft and the flywheel, rather than a clutch disk assembly. In this case, the flywheel is located on the output side of a vibration system whose boundary is a coil spring, and inertia on the output side is greater than with a conventional setup. As a result, the resonance engine speed can be set lower than the idle speed, affording very good damping performance. Thus, a structure including a combination of a flywheel and a damper mechanism is a two-mass flywheel or a flywheel damper (see, for example, Japanese Laid-Open Patent Application H4-231757). A flywheel fixed to the crankshaft of an engine is called a first flywheel, while a flywheel that is coupled to the crankshaft via an elastic member and to which a clutch device is mounted is called a second flywheel.